Angle indicator for aircraft



Aug.25, 1931. RR 1,820,791

I ANGLE INDICATOR FOR AIRCRAFT Filed May 3, 1929 muum INVENTOR WITNESS) EJFoyme-sl ATTORNEY Patented' Aug. 25, 1931 ROBERT J. FORREST, OF PORT ANGELES, WASHINGTON mom mmca'ron ron amcnar'r Application med lay a, 1929. Serial at. 380,211.

This invention relates to an instrument for use on aircraft to visually indicate the angle of inclination of the aircraft from the horizontal plane both with respect to its 5 longitudinal and transverse axes, and one visually denoting such angles at all times including conditlons of darkness, fog and storm.

The invention consists in the constructions, 1 arrangements and combinations of parts as described in the detailed specification following and as pointed out in the appended claims.

Briefly stated, the invention in its preferable form comprises a support mounting a hollow double walled approximately hemispherical spirit level with a transparent outer wall calibrated on the'lines of said longi-- tudinal and transverse axis in terms of angles of inclination and peripherally ringed in the zones of calibration to provide quadrants divided by the lines of said axes and ringed in zones of angles. .The interior of thehollow hemispherical body is illuminated and its inner wall is preferably translucent.

A preferred embodiment of the invention is shown in theaccompanying drawings forming part hereofand in which:

Figure 1 is a view in side elevation of the device as horizontally mounted upon a suit able support, in, for example, the cockpit of an airplane.

Figure 2 is a front elevation of the device as shown in Figure 1.

-Figure .3 is a'transverse vertical section taken on the line 3-3 of Figure 1.

Figure 4is atop plan view.

The device as shown comprises a support in the form of an angled bracket having a vertical. attachin back plate 5 depending from the rear e ge of afsubstantially circular horizontal base plate 6. The upper face of the base plate, as shown in Figure 3, is formed with an annular channel 7 around its outeredge and with a central depression 8' inwardly of saidchannel. The base 9 of the depression 8 is formed with a central 0 ning l0 therethrough for the insertion 0 an electric bulb 11 therethrough.

' of the base wit The opening 10 is closed by a plate 12 detachably clamped -to the base 9 by nuts 13 threading on studs 14 depending from the base 9 and mounted centrally thereof is a threaded socket 1 5 of conventional form receiving the threaded base of'the lamp bulb 11. Wires 16 conduct the lighting current to the socket 15 and lead out through an opening 17 in the back plate 5 to a source of current supply. The rear end of the base plate 6 is joined to the back or bracket plate 5 by diagonal brace bars 18 which may and preferably are formed integral therewith. The back plate isformed with a plurality of holes to receive attaching screws 20 or other fastening devices, and is intended for support in a vertical plane as by attachment to the vertical face of' a suitable support,

such for exam le as the instrument board in the pilots coc pit of an airplane.

Snugly fitting in the annular channel 7 late is the lower edge of a substantially emispherical hollow doubled walled spirit level generically indicated by 21. The inner wall 22 of the hemispherical body is of translucent matter, such as ground glass, to permit the light from the bulb 11 to netrate therethrough and is concentric and spaced from the outer wall 23 which is referably of'transtparent glass. The space etween the walls is lled with alcohol 24,; preferably colored, except for the usual bubble of air 25 as in all spirit levels.

The space between the inner and outer walls 22 and 23 at their bases within the channel? is closed by suitable leak proof packing 26 in the form of a cement not affected by the al cohol and effective to seal the base of the hemispherical body in the channel 7. A

filling opening maybe provided in the channel 7 and packing 26,-to receive a suitable sealing closure plug such as the screw whose head will effectively seal the opening.

The outer face of the transparent outer wall 23 is calibrated in terms of angles of inclination by concentric lines formed by pheripheral ridges 29 and arranged in quadrants spaced by lanes'representin the longitudinal and transverse axes of t e aircraft,

the lanes'designated 27, Fig. 4 representing facilitating visual angle determination.

With the aircraft on level or absolute horizontal keel, or in other words, with the lines of both its longitudinal and transverse axes in the horizontal plane, the-bubble 25 will appear at the top center of the hemisphere as shown in Figure If the nose of the aircraft is depressed and the longitudinal axis moved from the horizontal, the bubble will move rearwardly and lie in the ring zone 27 denoting the angle of downward inclination. If the downward inclination is accompanied by lateral inclination to the left, for example, the backwardly moving bubble will also move toward the right to the rin zone'in the line 28 of angle numerals denotlng the angle of inclination of its transverse axis with ,the quadrant formation of the indicating periphery of the outer-wall 23 enabling the pilot closelyto approximate by visual indication, the angular extent of lateral inclination.

Since the hemispherical spirit level is internalliy illuminated-by the bulb 1'1, and the colore spirit of the level offers a contrasting back ground for the whiteair bubble, the movement of the bubble and its indicating position will be easy to follow with the eye.

- The bracket mount for the hemispherical level body may be and preferably is cast as an integral unit of metal such as aluminum and the socket plate "12,- being removable, permits ready replacement of a bulb which burns out.

While the specific construction disclosed represents the preferred form of the invention, it is intended as illustrative rather than restrictive, and structural changes adapting the invention to different conditlons of manufacture and useare contemplated in consonance with thespirit of the invention and the scope of the appended claims.

'What I claim, therefore, and desire to secure by Letters Patent is:

1. An angle indicator for aircraft comprlsln a flat supporting base for mounting in a orizontal plane having an'annular channel in its upper face, a substantially hemispherical double walled hollow spirit level seated by its edges in said channel with said edges in the horizontal and parallel to the horizontal diameter of the hemispherical level, the inner wall of said level being of light transmitting material and the outer ,wall of' substantially transparent material,

fs'aid outer wall being visually divided by concentric hnes grouped in quadrants by hisecting lines at right angles denoting the longitudinal and transverse axes of the aircraft wit-l1 said concentric lines calibrated to denote angles of inclination from the horizontal planes of said longitudinal and transverse axes, and a level illuminating light radiating element mounted on said supporting base and positioned within the interior of the hollow hemispherical level.-

2. An angle indicator for aircraft com- ,n'isin a fiat base su )ort arran ed for mounting to lie in a horizontal plane and having an annulzn'channel in its upper face and an opening therethrough within said channel, 'a. plate detachably secured to the under side of said base support having a bulb socket thereon alined with said central opening and 'current conductors connected thereto, an electric light bulb detachably seating in said socket and extending upwardly from the face of said base support, and a hollow substantially hemispherical double wall spirit level superposed on said base support with the edges of its walls seating in said'annular channel and in the horizontal plane of support of the base and parallel 'to the horizontal diameter of its hemisphere, the space between said walls being closed by the base of said channels. 7

the inner wall of said hemispherical level being of translucent material and its outer wall being of substantially transparent material said outer wall being visually divided by concentriclines arranged in quadrants spaced by bisecting lines at right angles denoting the longitudinal and transverse axes of the aircraft, said lines being calibrated to denote angles of incl nation from the horizontal planes of said longitudinal'and transverse axes.

ROBERT J FORREST.

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